Temporal and spatial patterns of seed dispersal of four shrubs in a Cistus-Erica shrubland from Central Spain

Abstract

Abstract Background Species of Mediterranean shrublands regenerate after fires from persistent (PSSB) or transient (TSSB) soil seed banks, which can affect postfire regeneration owing to the different importance of the current seed crop depending on soil seed bank types. However, seed dispersal in these shrublands has been little investigated. Here, we recorded temporal and spatial patterns of seed dispersal in four shrubs with different soil seed banks (persistent soil seed sank, PSSB; transient soil seed bank, TSSB), three of them are seeders (Cistus ladanifer [PSSB], Salvia rosmarinus, [TSSB] and Erica umbellata [PSSB]) and one is a resprouter (Erica arborea [TSSB]) in an old (> 40 year.) shrubland in Central Spain. A 15 x 10 m plot was chosen and divided into a 0.5 x 0.5 m grid, where plant cover and density were measured. At 106 quadrats, seed traps were set and periodically (1–2 monthly) monitored for three years.Results S. rosmarinus dispersed in late spring-early summer, E. arborea dispersed during the summer, and C. ladanifer and E. umbellata dispersed since early summer until nearly late spring of the next year. Globally, seeds were being dispersed all year round. Seed crop varied between years although species differed in the year their seed crop was largest, despite large differences in climate. Seed rain and cover of each species were poorly related. Semivariogram analysis showed that seed dispersal expanded beyond the cover of each species a few meters. No association between seed crop size and spatial dependence was ascertained. While species dispersal tended to be negatively related to one another, E. arborea seeds tended to dominate underneath the other species.Conclusions Seed dispersal was consistent with the type of soil seed bank and postfire regeneration strategy: S. rosmarinus dispersed before the fire season; C. ladanifer and E. umbellata dispersed mostly after the fire season, which is coherent with a bet-hedging strategy against seed predators; E. arborea dispersed before the rainy season. The dominance of E. arborea seeds underneath the other species suggests that this midsuccessional species might dominate when openings form due to the deaths of the seeders standing plants, which have lower longevity.